The present invention relates to a device for a bottom unit for a projectile which can be fired through actuation by a propelling charge and which comprises a tubular part which contains a space for e.g. an illuminating or smoke charge attached to a parachute. At the firing of the projectile, the propelling charge is arranged to develop a gas pressure which actuates the projectile via the bottom unit, which is applied at one end of the tubular part and drives the projectile out of the barrel.
It is the intention that said illuminating or smoke charge, at a predetermined time after the firing of the projectile, is to be released and then ignited and, suspended in a parachute, fall to the ground. The bottom unit is then to be separable from the tubular part of the projectile when the charge attached to the parachute is expelled from the carrying part.
In order to avoid damage being caused by a separated bottom part to the parachute or its payload, it is known in the art to make a bottom plate eccentric, so that as a consequence of the angular rotation it obtains in the projectile around the line of symmetry, it is given a course that deviates from the course of the load carried by the parachute. However, it has been proved that the eccentricity of the bottom plate which is required in order that the deviation from the course shall be of the size desired, jeopardizes the function of the projectile itself. In order that the bottom plate shall withstand the high gas pressure to which it is subjected at the instant of firing, it must constitute a heavy and solid unit, and as a result of this the entire projectile will be eccentric in its rotation, i.e. it will rotate around an axis that deviates from the axis of symmetry. This can cause incorrect function of the time fuze which is preferably located in the nose of the projectile, resulting either in a failure to release the pyrotechnical charge, or a release of the charge at the wrong time.
To eliminate the above-mentioned disadvantages, it is known to make the bottom plate of a number of parts, the surfaces of the sections of which extend between the outside and inside of the plate, the bottom plate then being provided on its outside with a cover that extends at least over the sections between the parts of the bottom plate, and holds these together. The cover then also prevents gas from entering into the space through the sections. At the expulsion of the charge from the space in the projectile, the parts in the bottom plate will be thrown out from the course of the charge, each in a different direction, as a result of the centrifugal force that arises from the rotation of the plate around the axis of symmetry. The cover is particularly made light, so that it will be retarded considerably by the air resistance when the charge is expelled, which reduces the risk that it may damage the parachute.
In the case of heavy projectiles, however, in certain cases, it has been proved that the cover is not capable of keeping the parts of the bottom plate together sufficiently, resulting in internal displacements of the parts and, as a consequence of this, there will not be satisfactory obturation. To make the cover heavier would then not be an appropriate solution, as the cover would then be more likely to damage the payload after it has been expelled.